Design of Integrated Geothermal- Solar Based
System for Multigenerational Needs in a District
Energy System Application
Hamed Alimoradiyan
Submitted to the
Institute of Graduate Studies and Research
in partial fulfillment of the requirements for the degree of
Master of Science
in
Mechanical Engineering
Eastern Mediterranean University
July 2016
Approval of the Institute of Graduate Studies and Research
I certify that this thesis satisfies the requirements as a thesis for the degree of Master of Science in Mechanical Engineering.
We certify that we have read this thesis and that in our opinion it is fully adequate in scope and quality as a thesis for the degree of Master of Science in Mechanical Engineering.
1. Prof. Dr. Fuat Egelioğlu
2. Assoc. Prof. Dr. Hasan Hacışevki 3. Asst. Prof. Dr. Murat Özdenefe
Prof. Dr. Cem Tanova Acting Director
Assoc. Prof. Dr. Hasan Hacışevki Chair, Department of Mechanical Engineering
Assoc. Prof. Dr. Hasan Hacışevki Supervisor
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ABSTRACT
The current thesis proposes an integrated geothermal based multi-generation system including the triple effect LiBr/water absorption system (TEAS), organic Rankine cycle (ORC), air-conditioning system (dehumidification with cooling) and an electrolyzer. The aim of this system is to supply six outputs comprising heating, cooling, dry air, hot water, hydrogen, and power. All the simulations are done by Engineering Equation Solver software (EES). By inputting 500K geothermal water, the energetic and exergetic overall utilization factors (Ɛen and Ɛex) for the completely
multi-generation cycle would be 2.467 and 1.097, respectively. A parametric study was conducted indicating that a rise in the environment (ambient) temperature from 295K to 320K leads to an accumulative trend for exergetic coefficient of performance (COPex) while energetic coefficient of performance (COPen) remains
constant in TEAS. While, the evaporator temperature rises from 274K to 279K, there is a downward trend for COPen and COPex (from 1.491 to 1.479 and 0.3525 to
0.3145, respectively) as well as Ɛen and Ɛex. By raising the geothermal temperature
from 400K to 500K, Ɛen and Ɛex will increase from 2.354 to 2.467 and from 1.055 to
1.105, respectively. Moreover, the rise in geothermal temperature will upsurge the rate of hydrogen production as well as the heat rate in hot water production from 0.004873L/s to 0.005944L/s and from 8.365kW to 112.9kW, respectively. Moreover, environmental impacts, as one of the most designing parameter, are analyzed to find the system irreversibility (exergy destruction) and exergy losses. The parametric simulation is done to check the system in term of environmental suitability. In addition, a comparative study shows that using multi-generation cycle with higher
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COPen and COPex in comparison with conventional systems is more feasible to
design for reaching the six outputs.
Keywords: Geothermal, Multi-generation, Energy, Exergy, Overall Utilization
v
ÖZ
Bu çalışma çoklu jenerasyon sistemi ile üçlü etkili LiBr/su absorbsiyon sisteminin (TEAS) birleştirilmiş organik Rankin döngüsü (ORC), klima sistemi ( soğutma ile nem alma ) ve elektrolizer ile jeotermal tabanlı sistemlerin birleştirilmesini öngörmektedir. Bu sistemin amacı elde edilmesidin adet sonucun: ısıtma, soğutma, kuru hava, sıcak su, hidrojen ve gücün. 500K derecede jeotermal suyun enjekte edilmesi ile genel enerjik ve ekzerjik kullanım faktörleri (Ɛen ve Ɛex) sırası ile 2.467 ve 1.097 olacaktır. Üçlü etkili LiBr/su absorbsiyon sisteminin (TEAS) yapılan parametrik çalışma çevre ısısının 295K den 320K’e çıkması ekzerjik performans katsayısının (COPex) arttığını ancak enerjik performans katsayısının (COPen) ise sabit kaldığını göstermiştir. Dolayısı ile çevre sıcaklığı arttığında Ɛen sabit kalırken değişen her jeotermal kütle akışında Ɛen artacaktır, Bunun yanında buharlaştırıcı sıcaklığı 274K den 279K’e arttığında COPen ve COPex ( 1.491 den 1.479’a ve 0.3525 den 0.3145’e ) ayrıca Ɛen ve Ɛex sırası ile azalır. Soğutma yükü de 413.18kW’dan 410.4kW değerine düşerken klima sisteminde yoğunlaşan su miktarı artmaktadır. Jeotermal sıcaklığı 400K den 500K’e yükseltmekle Ɛen 2.354 den 2.467 ye ve Ɛex 1.055 den 1.105 ye sırası ile artacaktır. Ayrıca jeotermal sıcaklıktaki yükselme hidrojen üretim oranı 0.004873L/s den 0.005944L/s ye, sıcak su üretimindeki ısı oranını 8.365kW dan 112.9kW’a artıracaktır. Bunların yanında çevre etkisi de en önemli tasarım parametrelerinden biridir ve sistem geridönüşümsüzlüğünü ( ekzerji imhası ) ve ekzerji kayıplarını bulmak için analiz edilmiştir. Sistemin çevresel uygunluğu için parametrik simülasyon yapılmıştır. Ek olarak yapılan mukayese çalışması göstermiştir ki yüksek COPen ve COPex li çoklu
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generasyon döngüsü konvansiyonel sisteme göre istenen altı sonuca varmada daha uygulanabilir görülmektedir.
Anahtar kelimeler: Jeotermal, Çoklu jenerasyon, Enerji, Ekzerji, Genel kullanım
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ACKNOWLEDGMENT
I would like to record my gratitude to Assoc. Prof. Dr. Hasan Hacışevki for his supervision, advice, and guidance from the very early stage of this thesis as well as giving me extraordinary experiences throughout the work. Above all and the most needed, he provided me constant encouragement and support in various ways. His ideas, experiences, and passions have truly inspired and enriched my growth as a student. I am indebted to him more than he knows.
Special thanks go to Asst. Prof. Dr. Tahir Abdul Hussain Ratlamwala for his crucial contribution and guidance to this study.
Last but not the least; I would like to thank my family members specially my parents for all their supports throughout my life.
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TABLE OF CONTENTS
ABSTRACT………...…..……….iii ÖZ ………...…...………....v ACKNOWLEDGMENT………...….………vii LIST Of TABLES………..……...…….xi LIST OF FIGURES………...……...….xii LIST OF ABBREVIATIONS………..………xiv 1 INTRODUCTION……….………...……...…..………..…………1 1.1 Overview………..………..……....……….…...…11.2 Multi-generation Energy System………...……...…………3
1.3 Benefits of Multi-generation Cycles………..…………...…...……4
1.4 Aims and Objectives……….…………...………6
2 LITERATUREREVIEW………..…..…….8
2.1 Introduction………...… ……...……….8
2.2 Tri-generation Systems………..….………...……...…11
2.3 Multi-generation Energy Systems………..………...………13
3 DESCRIPTION OF THE SYSTEM…………..………...……….…16
4 MODEL DEVELOPMENT AND ANALYSIS…..……….………...……19
4.1 Thermodynamic Analysis………...………...………..………19
4.1.1 Exergoenvironmental Impact Factor……..………....………....20
4.1.2 Exergoenvironmental Impact Coefficient………...……...20
4.1.3 Exergoenvironmental Impact Index……...………...….20
4.1.4 Exergoenvironmental Impact Improvement………...20
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4.1.6 Exergetic Sustainability Index……….……...…20
4.2 Equations……….………….………...…...……21
4.2.1 Absorber Analysis………...……….………21
4.2.2 Low Temperature Heat exchanger Analysis……….…...……22
4.2.3 Pump 1 Analysis…………...………..……….…………23
4.2.4 Low Temperature Generator Analysis…………...…….……….24
4.2.5 Pump 2 Analysis…………...………..……...………….25
4.2.6 Moderate Temperature Heat Exchanger Analysis………...………26
4.2.7 Moderate Temperature Generator Analysis………….……...………….27
4.2.8 Pump 3 Analysis…………...………..………....…….28
4.2.9 High Temperature Heat Exchanger Analysis……….………….29
4.2.10 High Temperature Generator Analysis…………...…….29
4.2.11 High Temperature Condenser Analysis……….…..30
4.2.12 Moderate Temperature Condenser Analysis…….….……….31
4.2.13 Low Temperature Condenser Analysis…………..……….32
4.2.14 Evaporator Analysis………..…………...………...………33 4.2.15 Turbine Analysis …………...………...……….33 4.2.16 Condenser Analysis…………...……….……….34 4.2.17 Pump 6 Analysis…………...………..………....…….35 4.2.18 Boiler Analysis…………...……….………35 4.2.19 Electrolyzer Analysis…………...………...………36
4.2.20 Dehumidification System Analysis……….….37
5 RESULTS AND DISCUSSIONS………..……...40
5.1 Introduction………..…………...…………40
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6 CONCLUSIONS AND RECOMMENDATION …....………...…..……….58 REFERENCES………..…………...………...………61 APPENDIX………...………..……..69 Appendix A: Engineering Equation Solver Software Codes…….……….……..70
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LIST OF TABLES
Table 5.1: Evaluation of the current thesis results with the previous simulations done by other researchers………41
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LIST OF FIGURES
Figure 3.1: Multi-Generation System……….………..…...…...…18
Figure 4.1: Schematic of the TEAS Absorber…...………...…………..21
Figure 4.2: Schematic of the Low Temperature Heat Exchanger……...………..22
Figure 4.3: Schematic of the Pump 1 …...………...…….……..23
Figure 4.4: Schematic of the Low Temperature Generator …...……….……..24
Figure 4.5: Schematic of the Pump 2 …...………..………...…...……..25
Figure 4.6: Schematic of the Moderate Temperature Heat Exchanger …....…...…..26
Figure 4.7: Schematic of the Moderate Temperature Generator …...………..……..27
Figure 4.8: Schematic of the Pump 3 …...………...……..28
Figure 4.9: Schematic of the High Temperature Heat Exchanger …...………....…..29
Figure 4.10: Schematic of the High Temperature Generator ….……….….…..30
Figure 4.11: Schematic of the High Temperature Condenser …...…………..….…..30
Figure 4.12: Schematic of the Moderate Temperature Generator …...……....……..31
Figure 4.13: Schematic of the Low Temperature Condenser …...…………...……..32
Figure 4.14: Schematic of the Evaporator …...………...….………..33
Figure 4.15: Schematic of the Turbine …...………..…...………..33
Figure 4.16: Schematic of the Condenser…...………...……….…..……..34
Figure 4.17: Schematic of the Pump 6 …...………...…….………….….……..35
Figure 4.18: Schematic of the Boiler …...………..….…..35
Figure 4.19: Schematic of the Electrolyzer …...……….………..…….……….36
Figure 4.20: Schematic of the Dehumidification System …...……….……..37
Figure 5.1: Effects of Evaporator Temperature on COPen and COPex...……....……42
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Figure 5.3: Effect of Evaporator Temperature on ̇ and ̇ …...44
Figure 5.4: Effect of Specific Humidity on Air-conditioning Efficiency……..…...45
Figure 5.5: Effect of Specific Humidity on Utilization Factors………...…...46
Figure 5.6: Effect of Geothermal Water Temperature on Ɛen and Ɛex…….……...47
Figure 5.7: Effect of Geothermal Temperature on ̇ and ̇ ……....…...……..48
Figure 5.8.: Effect of Geothermal Temperature on ̇ and ̇ … ... 49
Figure 5.9: Effects of Ambient Temperature on COPen and COPex………...……50
Figure 5.10: Effect of Ambient Temperature on Ɛen and Ɛex…..……...…..….……...51
Figure 5.11: Effects of Variation Evaporator Temperature on Exergoenvironmental Impact factor………….………...….………….…….52
Figure 5.12: Effects of Variation Evaporator Temperature on Exergoenvironmental Impact Coefficient ………....………...…………..53
Figure 5.13: Effects of Variation Evaporator Temperature on Exergoenvironmental Impact Index………..……..…….………..54
Figure 5.14: Effects of Variation Evaporator Temperature on Exergoenvironmental Impact Improvement………..………..……...………55
Figure 5.15: Effects of Variation Evaporator Temperature on exergetic stability factor index………..….…….…….………56
Figure 5.16: Effects of Variation Evaporator Temperature on the exergetic sustainability ………...…...………57
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LIST OF ABBREVIATIONS
COP Coefficient of Performance ̇ Exergy Destruction Rate (kW)
̇ Energy Rate (kW) ̇ Exergy Rate (kW) H Specific Enthalpy, kJ/kg
HW Hot Water
̇ Mass Flow Rate (kg/s) P Pressure (kPa)
̇ Heat Flow Rate (kW) T Temperature (K) S Specific Entropy (kJ/kg K) ̇ Work Amount (kW) Greek letters Η Efficiency ω specific Ratio (%)
ε Overall Utilization Factor
Subscripts Abso Absorber Cond Condenser En Energy Ex Exergy Eva Evaporator Geo Geothermal
xv HHX High Temperature Heat Exchanger HTG High Temperature Generator HW Hot Water
H2 Hydrogen
LHX Low Temperature Heat Exchanger LTG Low Temperature Generator
MHX Medium Temperature Heat Exchanger MTG Medium Temperature Generator P Pump Ph Physical Turb Turbine W Water X Concentration of Ammonia–Water 1,. . .,46 State Numbers
0 Ambient or Reference Condition
Acronyms
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Chapter 1
INTRODUCTION
1.1 Overview
Nowadays, by considering the size of mega-cities and high rate of population growth all around the world, energy consumption has become a crucial concern for nations around the world. The high pace development in the industrial era has enhanced the energy demand more than before in the last decades. To supply energy needs in the recent years, using fossil fuels including the environmental impacts such as emitting greenhouse gasses, global warming, and ozone depletion, have become increased because of their high efficiency performance and accessibility.
Global warming, as one of the important environmental threats, clarifies to an increase in the temperature average of the environment, which has been peered recently and it is raising so fast these days, Green (environmental) activities are trying to find new techniques and ways to defeat the atmospheric problem including greenhouse gases (GHGs) and aerosols. A greenhouse gas in the atmosphere can absorb the sun radiation and release it as infrared waves [1]. Global warming is directly affected by GHGs.
The global warming can be created by the following reasons [2]:
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Carbon dioxide emitted from transportation systems because of burning gasoline
Methane can be produced by animals, agricultural activities, and from sea beds
Destroying forests especially in tropical areas to produce wood, pulp and making farmland
Using chemical fertilizer on croplands
It has become so crucial to define new ways to supply energy demands like alternative energy sources, which are energy efficient and environmentally friend without harmful impacts on the nature and its living creatures [3].
Integrated energy system refers to a system that is capable to drive a multi-generation energy cycle to produce heating load by using two or more initial energy resources. In a cogeneration cycles, overall energy efficiency is the portion of the input energy to the exit amount of the electricity and thermal energy, is near to the 50% [4].
Lately, combined heat and power energy systems (CHPs), that are capable to produce heating and power, have been up graded and extended to the tri-generation systems by the energy researchers to produce three useful outputs including thermal energy, cooling and power generation from a basic energy. These systems use the output waste heat of utilities to improve the overall thermal efficiency [5]. The cooling and heating equipment in a tri-generation system can be run by the extra heat from system’s impetus [6].
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The produced heat can be used for heating process (steam production) or domestic hot water and space heating. In addition, the absorption chiller can produce cooling by the injection of the produced heat. Tri-generation systems can be utilized in several aspects such as domestic usage, hospitals, airports, hotels, food industries and chemical process. The next step in this science is generation Cycles. Multi-generation is a system with higher variety of outputs in comparison with tri-generation systems. A multi-tri-generation system is capable to generate power process heat, cooling, hydrogen, dried air, and water desalination. In multi-generation cycles, the efficiency is significantly higher than CHPs and trig-generation systems due to its extra outputs (water desalination, hydrogen, etc.). In order to produce hydrogen, it is needed to install an electrolyzer that requires electricity. The heating load is referred to two parts of space heating and hot water production. Absorption system receives available waste heat rejected to produce cooling for the domestic purpose and cooling for the air-drying systems or chillers. To produce drinkable fresh (potable) water from multigeneration energy system, it is needed to consider desalination equipment. In this way, a part of the produced or waste heat is used to drive the desalination system, and a portion of the generated electricity is used to run the moving pumps.
1.2 Multi-generation Energy System
Multi-generation energy system refers to a system which is capable to produce more than three outputs with the same prime mover. These outputs can be electricity, heating, cooling, hydrogen, dry air and hot water. This system can be installed for residential, commercial and some other places that several useful outputs are needed. In order to design a multi-generation system, its location, type initial source and number of needed outputs should be considered. These systems are considered as a
4
solution of global warming and environmental concerns. The optimization methods can be considered in designing process to increase the system efficiency.
1.3 Benefit of Multi-generation Cycles
Multi-generation energy systems can be so useful and beneficial due to some parameters such as less waste and thermal losses, higher energy and exergy efficiency, less greenhouse gas emissions, less operating expenses, better resource usage, shorter delivery units, and several multiple-production choices [7].
These points are discussed in more details below. Multi-generation design increases the total energy and exergy efficiency of the utility and decreases the operation and maintenance costs. The overall energy efficiency of the conventional utilities that burn fossil fuels in a lone main impetus is generally around 40%. It shows that about half of the thermal energy injected to a primary energy system will be the waste energy and not used in any parts. The total energy efficiency of the primary utility that generates the heat and electricity in parallel can be near to the 60% [8].
It is inevitable that by using the thermal losses and waste heat from the main parts of the system, the overall energy efficiency of the power the multi-generation systems can reach up to 80% [9]. In a multi-generation energy system, the thermal energy heat produced by some renewable resources is used to run absorption system to produce heating and cooling but in a conventional utility fuel injection is needed to run the system. Therefore, a multi-generation power plant has higher overall performance compared to other power generation systems.
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The efficiencies of multi-generation systems are higher compared to other power generation systems. Therefore, it can be said that multi-generation systems are friendly to the environment.
By considering some important limitation of designing multi-generation utilities in the distribution parts due to their internal dangerous emissions. Smaller delivery parts in multi-generation cycles causes less costs and energy losses that can be considered as other benefits of a multi-generation power plant. The primary production of electricity is van be gotten from the nearest point to the users and from a centralized power plant. The efficiency drops about 9% because of the transmission and distribution from the base plant to the city [9]. The mentioned points and benefits of the multi-generation energy systems encourage the scientists and designer to step more in this field to solve the vague aspects. This higher overall energy efficiency apart from exergy efficiency is often the major factor in using multi-generation power plants. Before selecting any kind of multi-generation energy systems, additional assessments including calculation of initial capital and operation costs, is needed to guarantee efficient and economic multi-generation plant construction [8].
Geothermal water is one of the common renewable energy sources analyzed in details by researchers all around the world, which is capable to supply the sustainable and green energy for the needed demands. After finding the geothermal energy benefits and huge energy capacity, its usage has raised more than double as stated by several researchers [10]. The main limitation of using geothermal water energy is its different temperature by considering its location; so the needed temperature should be considered before choosing this type of energy source for the utilities.
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There are three types of geothermal energy sources that are low temperature geothermal source (below 90°C), moderate temperature geothermal source (90– 150°C) and high temperature geothermal source (above 150°C) [11]. Moderate-temperature geothermal energy source can supply the needed thermal energy to drive the Organic Rankine cycles, or they can be used to provide the needed heating and cooling using in absorption cooling equipment. The low-temperature geothermal energy source is the most suitable one as a direct heating source [12].
Useful and efficient ways to use geothermal sources has become so popular among the researchers and many articles have been published related to these interesting topics [13-15].
For those moderate and low temperature geothermal energy sources, it is much more suitable to use them directly for the heating and cooling purpose. Nevertheless, combination of the heat and power production from any kind of energy sources is always useful and helpful [16-18]. Combination of the heat and power (CHP) system is capable to produce both thermal energy and electricity generally in the shape of steam or hot water, and electricity [19].
1.4 Aims and Objectives
The novelty of this master thesis is to largely model and analyze a geo-thermal based multi-generation energy system by engineering equation Solver software (EES). In addition, energy, exergy and environmental impact assessment are conducted to improve the performance analysis of the system. In this study, a geothermal power plant integrated with TEAS, electrolyzer, and organic Rankine cycle is considered
7
for cooling, heating, hot water, hydrogen, and power production. This master research thesis is including of some main objects as below:
a) To extend the mathematical model for the designed multi-generation energy system:
Complete thermodynamic modeling of a multi-generation system integrated to geothermal energy as initial energy resource, an electrolyzer device to produce hydrogen production, a triple effect absorption chiller, dehumidification system and an organic Rankine cycle.
b) To achieve the exergy analysis of each multi-generation subsystem: - Exergy analysis of the stream flow rate in each subsystem
- Calculation of the exergy destruction rate and exergy efficiency for the components.
c) To determine the system in aspect of its harmful effects on the environment and atmosphere
- Determination of environmental sustainability index (the system harmful effect on the environment) and finding the relation between exergy and environmental impacts.
d) To perform a complete parametric study and the performance assessment of the system.
- determination of a separate parametric study for each subsystem to achieve the effect of design parameter on the system performance such as environmental impacts and exergy efficiency.
- Effect of environment condition on the performance assessment of each subsystem.
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Chapter 2
LITERATURE REVIEW
2.1 Introduction
In this section, a comprehensive study of the power plants using multi-generation energy system is illustrated. In addition, the various studies related to the CHPs and tri-generation energy systems are presented in this literature. In this chapter, a brief of the related papers including their methods of analyzing and their studies are presented. In addition, it is tried to cover the recent studies done by the researchers related to the multi-generation, tri-generation and cogeneration energy systems. The literature has been divided to the some parts depends on the thermodynamic modeling, energy, exergy of all the types of energy systems including cogeneration, tri-generation and multi-generation. The literature starts with the literature details then provides a view about recent related studies.
Recently, due to environmental concerns because of using fossil fuels in the power plants, defining new techniques to produce multiple outputs from a constant prime source has been become so popular by the governments. Utilities with multiple outputs can be defined to be capable to produce several outputs from the single or multiple energy inputs. The aim to design a multi-generation energy system is to increase the energy and exergy efficiency of the utility and decrease the environmental impacts at the same time. A multi-generation energy system can produce electricity, heating, cooling, hot water, hydrogen and dry air by the
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dehumidification system. In a more simple way, cogeneration energy systems (combined heat and power) provide two products including thermal energy and electricity power. CHP energy cycles efficiency can be found from dividing the injected energy to the system by both cycle production (heats and electricity) and it is generally around 40-50% or higher in some cases [8].
Huangfu et al. [20] studied a stand-alone energy system for the building needs such as thermal energy, cooling load and electricity integrated to an absorption system as an experimental case. They analyzed the absorption chiller performance under different heating conditions. The authors could prove that there is a linear relation between the injected hot water temperature and absorption system for the two different systems. In a commercial case, CHP-ORC systems analyzed and optimized by Mago et al. [21]. As a residential case, an integrated CHP system with the storage capacity of the thermal and electric energy, studied by Bianchi et al. [22]. Energy efficiency evaluation and energy saving methods analyzed to solve the vague problems of energy efficiency for a combined cold, heat and electricity production system done by Havelsky [23].
Heat pumps was experimented to analyze the energy performance of a tri-generation utility by Miguez et al. [24-25]. This study could prove, heat pumps can increase the energy efficiency of the system.
Khaliq et al. [7] analyzed a system including refrigeration cycle and electricity in aspect of exergy performance and did a comprehensive analysis to determine the result of pitch point, gas type and exhaust gas inlet temperature on electricity, exergy destruction rate and energy-exergy efficiency for a combined cogeneration system.
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In a case study located in Turkey, Cihan et al. [26] analyzed energy and exergy performance of a combined energy system to reduce the exergy destruction for a CHP. The proposed study could show that main part of the exergy destruction (near to 85%) is directly related to the gas turbine, heat recovery steam generators (HRSGs) and combustion chamber.
A Proton Exchange Membrane (PEM) fuel cell is considered to find the exergy analysis result for a residential CHP by Barelli et al. [27]. They also could achieve to the comprehensive inclusive study to find out results of fuel cell parameters including specific humidity, temperature and pressure on the system. A suitable high efficiency multi-generation system for the residential application was exergetic analyzed by Bingol et al. [28].
Both energetic and exergetic analysis of CHP energy cycle using fuel cell device and a gas turbine is done by El-emam and Dincer [29]. To reach the suitable system performance, they did comprehensive simulation to check the system by varying some major and effective factors. The analysis results showed that molten carbonate fuel cell (MCFC) systems could reach to the 3.14 kW as the maximum output power at the operation temperature range of 600-650°C. The total energy and exergy efficiencies can reach to 42.89% and 37.75%, respectively. A complete parametric study and hybrid CHP (using SOFC) linked to gas turbine is done by Akkaya et al. [30]. It is achieved from their results that entropy generation rate is affected by the exergy performance coefficient of the system. Al-sulaiman et al. [31] showed that the efficiency can be increased up to 22% by using tri-generation energy system integrated with an energy cycle.
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They could prove that maximum efficiency for the tri-generation energy system, heating cogeneration system, cooling cogeneration system and net electricity generation can reach to 74%, 70%, 57% and 46%, respectively. In addition, they presented that exergy analysis is a power tool to determine the maximum power of the CHP or tri-generation energy systems.
2.2 Tri-generation Systems
The tri-generation systems are capable to produce electricity, heating and cooling with the same initial input energy source. The overall efficiency can be improved by using the waste heat of the power plant and free energy can be obtained for the waste energy. In these energy systems, the heating and cooling equipment can be driven by using the waste thermal energy released from prime movers [6]. The produced heat can be used for heating needs, steam producing and to heat the domestic water sources. The output heat also can be used to run the absorption system for air conditioning purpose. Popisisl et al. [32] did the comparative study for the mention energy systems and checked their results for a residential application. The results achieved to the point that cogeneration energy systems can increase the overall energy efficiency of a single generation system up to 31% while tri-generation system can raise the efficiency up to 39% in the same initial conditions. Three types of tri-generation systems including solar-trigeneration, Solfi oxide fuel cell (SOFC)-tri-generation and biomass-trigeneration were compared by Al-sulaiman et al. [33].
Influence of the main parameters on the thermodynamic performance of tri-generation energy systems analyzed by Martins et al. [34]. A planning parameter” equivalent gas price” defined by Chicco and mancarella [35] by installing some especial energy sensors to check the fuel heating value and efficiency of the energy
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systems. Thermodynamic assessment on a tri-generation energy system done by Minciuc et al. [36] to define a new model for evaluating the system and find the limitations to link a gas turbine to reach the maximum performance.
Buck and Fredmann [37] analyzed system working results of a tri-generation energy system including a small-size solar energy system and a micro turbine. They showed that in a comparative study of single and double effect absorption system, in term or economics points, using double effect absorption system is more suitable because it can work in higher energy efficiency with the lower operation and maintenance expenses.
Exergy analysis is a helpful and powerful tool to determine the type and location of the exergy losses which can occur in the form of exergy destruction or emitted waste exergy [38]. Therefore, exergy analysis can show the best way to design and define the needed strategies for the energy system development. Recently, exergy has become more and more popular to assess the energy and thermal systems. Khaliq [39] analyzed the tri-generation energy system in term of exergy. The considered system is including an absorption system (single effect) to generate cooling loads, turbine, and primary heat recovery steam generator to supply the thermal energy. In addition, he did a complete parametric study to check the main parameter effects on the system performance. The results showed that combustion chamber and steam generator are the most important factors for the exergy destruction that cause high rate of exergy destruction in the system performance. Ahmadi et al. [6] showed an exergoenvironmental assessment of a tri-generation energy system connected to a gas turbine and organic Rankine cycle (ORC), and did a complete parametric study including the major factors in the tri-generation system.
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Mago and Hueffed [40] analyzed a combined cooling; heating and power (CCHP) energy system linked to a turbine as a commercial office application and varies the operation parameters to find the amount of Carbon emission to calculate the Carbone reduction in using the CCHP energy systems. Many publications are available considering the environmental assessments of the energy systems. A hydrogen and fuel cell system are examined in term of environmental and sustainability points by Dincer [41], and Dincer and Rosen [38]. In addition, environmental evaluation of a dehumidification system is conducted [42].
2.3 Multi-generation Energy Cycles
This kind of system is defined as an energy cycle to produce multiple different outputs in comparison with tri-generation systems. It can generate heating, cooling, hydrogen, hot water electricity and dried air by the same initial energy injection. It is crucial to design these systems for the places with the high rate of demands such as residential areas, power plants, hotels, etc. as the most important factor to design a multi-generation energy system is to consider the enough construction area.
Hosseini et al. [43] designed and analyzed thermodynamically an integrated multi-generation system. The system is including of multi effect desalination, a primary heat recovery steam generator (HRSG) and a gas turbine to generate fresh water, thermal energy, cooling loads and electricity. This study also conducted an inclusive analysis was done to check the main parameters results on the system performance. They could also indicate that integrating energy cycles can raise the overall efficiency up to 25%.
14
A novel simulation of a tri-generation utility including of an organic Rankine cycle, a single effect absorption system, a gas turbine and recovery steam generator (double pressure) analyzed by Ahmadi et al. [6]. They presented a complete study analysis to check the results of the main factors on the system. The outputs of the study indicated that cycle performance is significantly affect by the gas turbine isentropic efficiency, turbine inlet temperature and compressor pressure ratio.
An integrated photovoltaic thermal (PV/T) and absorption system to produce hydrogen and cooling production studied by Ratlamwala et al. [44]. In addition, parametric study was done on the different electrolyzer working hour, sun irradiations, PV area and inlet air temperature on the hydrogen and power production.
Ratlamwala et al. [45] studied a novel simulation on a multi-generation energy cycle using geothermal as inlet energy source linked to double flash power generating unit and using ammonia/water as the working fluid, absorption system and electrolyzer. Output power, hydrogen production can be increased by raising the inlet geothermal temperature, mass flow and pressure. A solar-based multi-generation cycle with hydrogen production including of electrolyzer, ORC, absorption chiller, designed and analyzed by Ozturk and Dincer [46]. The results showed that using parabolic trough dishes has the highest rate of exergy destruction in comparison with other types (lower overall exergy efficiency).
Dincer and Zamfirescu [7] presented a complete energy and exergy analysis of a renewable-energy-based multi-generation system to produce hydrogen, cooling, heating, hot water, electricity and dried air. The scientists and researchers
15
recommend that using integrated multi-generation (especially energy systems integrated to renewable sources) can be useful to come up with a solution to increase the overall energy and exergy efficiency of the energy systems and decrease the environmental impacts to save the nature and its creatures.
16
Chapter 3
DESCRIPTION OF THE SYSTEM
The system including integrated triple effect LiBr/water absorption with organic Rankine cycle, an electrolyzer, and an air conditioning system, which is presented in the current research, is illustrated in Figure 3.1. The proposed energy system is capable to generate six valuable productions, namely electricity (power), thermal energy, hot water, cooling loads, hydrogen and conditioned air (dry air). A geothermal energy source is selected to as the energy carrier of the system by going over the TEAS to generate heating, cooling, and hot water, as presented in Figure 3.1.
Total heating and cooling production (by TEAS) are then tansported to the residential areas. The exiting geothermal water from TEAS then will pass through the solar collector to increase its temperature at state 29 and will enter the ORC boiler to vaporize the ammonia to produce power for the hydrogen production unit besides the buildings. It should be noted that the cold level of the sea has been used to decrease the condenser temperature in organic Rankine cycle (ORC) at state 38. After that, the geothermal water will leave the boiler at state 31 and will supply the domestic hot water for the buildings.
The cooling production is separated into two parts. One share is provided for domestic purposes of the buildings, and the other portion is sent for the
17
conditioning devices to deliver chilled and dried air to cold loadings. The produced hydrogen is kept in the tank chambers and can be used advanced as the needed amount by the consumer. As shown in Figure 3.1, the air conditioning system that is measured in the current thesis is cooling load through dehumidification for supplying cooled dry air. The humid air flows to the dehumidification system at state 41, passes into the cooling coil where it meets cooled coils. The cooled coils condense the humid air and help it in losing wetness. Then dried and conditioned air leaves the system to supply in the dry cold tanks.
18 F ig u re 3.1: Mult i-ge ne ra tion s y stem
19
Chapter 4
MODEL DEVELOPMENT AND ANALYSIS
4.1 Thermodynamic Analysis
To examine the proposed integrated system, energetic and exergetic analyzes were considered. The energy, exergy, and mass balance equations are written for each component of TEAS and the ammonia Rankine thermodynamic cycle. Also, the efficiency of the Rankine cycle and COPs of TEAS equations are calculated. The system is assumed to be working under thermodynamic steady state conditions. Heat loss and pressure drops in heat exchangers and the connecting piping system are also considered negligible. Moreover, the parasitic losses (from the solar collectors) produced by the pumps and turbines are measured in calculating the net power output from the plant. Finally, the heat exchangers are modeled on the principle of temperature change and for each heat exchange of TEAS, the temperature change is considered constant.
In addition, by calculating and considering the exergy efficacy and exergy destruction, the exergoenvironmental analysis can be obtained to analyze their impacts on the environments. This analysis is including of six main parameters that are listed as below.
20
4.1.1 Exergoenvironmental Impact Factor
The exergoenvironmental impact factor determines the positive effect of the investigated system on the environment. The purpose of studying this parameter is that it helps in reducing the environmental impact of the system by decreasing the irreversibilities in the system.
4.1.2 Exergoenvironmental Impact Coefficient
The exergoenvironmental impact coefficient is related to the exergetic efficiency of the system.
4.1.3 Exergoenvironmental Impact Index
The exergoenvironmental impact index is an important parameter to study as it indicates whether the system under investigation damages the environment due to its unusable waste exergy output and exergy destruction.
4.1.4 Exergoenvironmental Impact Improvement
The exergoenvironmental impact improvement parameter helps finding the environmental appropriateness of the investigated system.
4.1.5 Exergetic Stability Factor
The exergetic stability factor is a function of the desired output exergy, total exergy destruction, and exergy carried by unused fuel.
4.1.6 Exergetic Sustainability Index
The exergetic sustainability index is the multiplication of exergetic stability factor and exergoenvironmental impact improvement of the system.
21
4.2 Equations
Energy, Exergy Analyzes and Environmental Impacts Assessment are illustrated below.
4.2.1 Absorber Analysis
Figure 4.1 illustrates schematic of the absorber. (Also, see Figure 3.1).
Figure 4.1: Schematic of the absorber
The following equations are used for the absorber.
1
* h
1m * h
10 10m * h
6 6 AbsQ
m
(1) ,Abs(1
0/
) *
q avg AbsEx
T
T
Q
(2) 1 6 10(
) / 3
avgT
T
T
T
(3) , 10 6 1 ,Abs d Abs qEx
Ex
Ex
Ex
Ex
(4) WhereQ
Abs,m
i,Ex
q,Abs,T
0,T
avg,Ex
d Abs, andEx
ipresents absorber heat flow rate, mass flow, thermal exergy rate, ambient temperature, average temperature, exergy destruction rate, and sate exergy rate , respectively.22
4.2.2 Low Temperature Heat exchanger Analysis
Figure 4.2 illustrates schematic of the low temperature heat exchanger. (Also, see Figure 3.1)
Figure 4.2: Schematic of the low temperature heat exchanger
The following equations are used for the low temperature heat exchanger.
4
* h
4m * h
5 5 LHEQ
m
(5) ,LHE(1
0/
) *
q avg LEHEx
T
T
Q
(6) 4 2 3 5
(
) / 4
avgT
T
T
T
T
(7) ,LHE 2 4 5 ,LHE 3 d q
Ex
Ex
Ex
Ex
Ex
Ex
(8) Where
Q
LHE,m
i,Ex
q,LHE,T
0,T
avg,Ex
d,LHE andEx
ipresents low temperature heat exchanger heat flow rate, mass flow, thermal exergy rate, ambient temperature, average temperature, exergy destruction rate, and sate exergy rate , respectively.23
4.2.3 Pump 1 Analysis
Figure 4.3 illustrates schematic of the pump 1. (Also, see Figure 3.1)
Figure 4.3: Schematic of the pump 1
The following equations are used for the pump 1.
,1
(
1*
1* (
2 1)) /
isentropicpump
W
m
v
P
P
(9)
1 pump,1 2 d pump, ,1
Ex
W
Ex
Ex
(10) Where
W
pump,1,m
i,v
1,P
2,
isentropic,Ex
d pump, 1 andEx
ipresent pump work, mass flow, specific volume, pressure, isentropci efficency, exergy destruction rate and sate exergy rate , respectively.24
4.2.4 Low Temperature Generator Analysis
Figure 4.4 illustrates schematic of the low temperature generator. (Also, see Figure 3.1)
Figure 4.4: Schematic of the low temperature generator
The following equations are used for the low temperature generator.
4
* h
4m * h
20 20m * h
7 7 LTGQ
m
(11) ,LTG(1
0/
) *
q avg LTGEx
T
T
Q
(12) 4 20 7
(
T ) / 3
avgT
T
T
(13) , 20 4 ,LTG 7 d Abs q
Ex
Ex
Ex
Ex
Ex
(14) Where
Q
LTG,m
i,Ex
q,LTG,T
0,T
avg,Ex
d,LTG andEx
ipresents low temperature generator heat flow rate, mass flow, thermal exergy rate, ambient temperature, average temperature, exergy destruction rate, and sate exergy rate , respectively.25
4.2.5 Pump 2 Analysis
Figure 4.5 illustrates schematic of the pump 2. (Also, see Figure 3.1)
Figure 4.5: Schematic of the pump 2
The following equations are used for the pump 2.
,2
(
3*
3* (
11 3)) /
isentropicpump
W
m
v
P
P
(15)
3 pump,2 11 d pump, ,2
Ex
W
Ex
Ex
(16) Where
W
pump,2,m
i,v
3,P
i,
isentropic ,Ex
d pump, 2 andEx
ipresent pump work, mass flow, specific volume, pressure, isentropic efficieny, exergy destruction rate and sate exergy rate , respectively.26
4.2.6 Moderate Temperature Heat Exchanger Analysis
Figure 4.6 illustrates schematic of the moderate temperature heat exchanger. (Also, see Figure 3.1)
Figure 4.6: Schematic of the moderate temperature heat exchanger
The following equation are used for the moderate temperature heat exchanger.
19
* h
19m * h
18 18 MHEQ
m
(17) ,MHE(1
0/
) *
q avg MHEEx
T
T
Q
(18) 18 11 12 19
(
) / 4
avgT
T
T
T
T
(19) ,MHE 11 18 12 ,MHE 19 d q
Ex
Ex
Ex
Ex
Ex
Ex
(20)
Where
Q
MHE,m
i,Ex
q,MHE,T
0,T
avg,Ex
d,MHE andEx
ipresent moderate temperature heat exchanger heat flow rate, mass flow, thermal exergy rate, ambient temperature, average temperature, exergy destruction rate, and sate exergy rate , respectively.27
4.2.7 Moderate Temperature Generator Analysis
Figure 4.7 illustrates schematic of the moderate temperature generator. (Also, see Figure 3.1)
.
Figure 4.7: Schematic of the moderate temperature generator
The following equation are used for the moderate temperature generator.
24
* h
24m * h
17 17 18* h
18 MTGQ
m
m
(21) ,MTG(1
0/
) *
q avg MTGEx
T
T
Q
(22) 18 17 24
(
) / 3
avgT
T
T
T
(23) ,MTG 17 24 ,MTG 18 d q
Ex
Ex
Ex
Ex
Ex
(24) Where
Q
MTG,m
i,Ex
q,MTG,T
0,T
avg,Ex
d,MTG andEx
ipresent moderate temperature generator heat flow rate, mass flow, thermal exergy rate, ambient temperature, average temperature, exergy destruction rate, and sate exergy rate , respectively.28
4.2.8 Pump 3 Analysis
Figure 4.8 illustrates schematic of the pump 3. (Also, see Figure 3.1)
Figure 4.8 illustrates schematic of the pump 3
The following equations are used for the pump 3.
,3
(
12*
12* (
13 12)) /
isentropicpump
W
m
v
P
P
(25)
12 pump,3 13 d pump, ,3
Ex
W
Ex
Ex
(26) Where
W
pump,3,m
i,v
12,P
i,
isentropic,Ex
d pump, 3 andEx
ipresent pump work, mass flow, specific volume, pressure, isentropic efficiency, exergy destruction rate and sate exergy rate , respectively.29
4.2.9 High Temperature Heat Exchanger Analysis
Figure 4.9 illustrates schematic of the high temperature heat exchanger. (Also, see Figure 3.1)
Figure 4.9: Schematic of the high temperature heat exchanger
The following equations are used for the high temperature heat exchanger.
15
* h
15m * h
16 16 HHEQ
m
(27) ,HHE(1
0/
) *
q avg HHEEx
T
T
Q
(28) 14 15 12 16
(
) / 4
avgT
T
T
T
T
(29) ,HHE 12 15 14 ,HEE 16 d q
Ex
Ex
Ex
Ex
Ex
Ex
(30) Where
Q
HHE,m
i,Ex
q,HHE,T
0,T
avg,Ex
d,HHE andEx
ipresents high temperature heat exchanger heat flow rate, mass flow, thermal exergy rate, ambient temperature, average temperature, exergy destruction rate, and sate exergy rate , respectively.4.2.10 High Temperature Generator Analysis
Figure 4.10 illustrates schematic of the high temperature generator. (Also, see Figure 3.1)
30
Figure 4.10: Schematic of the high temperature generator
The following equations are used for the high temperature generator.
27
* c
p,27(T
27T )
28 HTGQ
m
(31) ,HTG(1
0/
) *
q avg HTGEx
T
T
Q
(32) 14 15 21
(
) / 3
avgT
T
T
T
(33) ,HTG 14 15 21 ,HTG d q
Ex
Ex
Ex
Ex
Ex
(34) Where
Q
HTG,m
i,Ex
q,HTG,T
0,T
avg,Ex
d,HTG andEx
ipresent high temperature generator heat flow rate, mass flow, thermal exergy rate, ambient temperature, average temperature, exergy destruction rate, and sate exergy rate , respectively.4.2.11 High Temperature Condenser Analysis
Figure 4.11 illustrates schematic of the high temperature condenser. (Also, see Figure 3.1)
31
The following equations are used for high temperature condenser.
21
* h
21m * h
22 22 HTCQ
m
(35) ,HTC(1
0/
) *
q avg HTCEx
T
T
Q
(36) 21 22
(
) / 2
avgT
T
T
(37) ,HTC 21 22 ,HEE d q
Ex
Ex
Ex
Ex
(38) Where
Q
HTC,m
i,Ex
q,HTC,T
0,T
avg,Ex
d,HTC andEx
ipresent high temperature condenser heat flow rate, mass flow, thermal exergy rate, ambient temperature, average temperature, exergy destruction rate, and sate exergy rate , respectively.4.2.12 Moderate Temperature Condenser Analysis
Figure 4.12 illustrates schematic of the moderate temperature condenser. (Also, see Figure 3.1)
Figure 4.12: Schematic of the moderate temperature condenser
The following equations are used for moderate temperature condenser.
24
* h
24m * h
23 23m * h
25 25 MTCQ
m
(39) ,MTC(1
0/
) *
q avg MTCEx
T
T
Q
(40) 24 23 25
(
) / 3
avgT
T
T
T
(41) ,MTC 23 24 ,HEE 25 d q
Ex
Ex
Ex
Ex
Ex
(42)
32
Where
Q
MTC,m
i,Ex
q,MTC,T
0,T
avg,Ex
d,MTC andEx
ipresent moderate temperature condenser heat flow rate, mass flow, thermal exergy rate, ambient temperature, average temperature, exergy destruction rate, and sate exergy rate , respectively.4.2.13 Low Temperature Condenser Analysis
Figure 4.13 illustrates schematic of the low temperature condenser. (Also, see Figure 3.1)
Figure 4.13: Schematic of the low temperature condenser
The following equations are used for low temperature condenser.
26
* h
26m * h
7 7m * h
8 8COND
Q
m
(43),
(1
0/
) *
q COND avg COND
Ex
T
T
Q
(44) 8 26 7
(
) / 3
avgT
T
T
T
(45) ,COND 7 26 ,HEE 8 d q
Ex
Ex
Ex
Ex
Ex
(46) Where
Q
COND,m
i,Ex
q,COND,T
0,T
avg,Ex
d,COND andEx
i present low temperature condenser heat flow rate, mass flow, thermal exergy rate, ambient temperature, average temperature, exergy destruction rate, and sate exergy rate , respectively.33
4.2.14 Evaporator Analysis
Figure 4.14 illustrates schematic of the evaporator. (Also, see Figure 3.1)
Figure 4.14: Schematic of the evaporator
The following equations are used for the evaporator.
10
* h
10m * h
9 9 EVAPQ
m
(47) ,EVAP(1
0/
) *
q avg EVAPEx
T
T
Q
(48) 9 107
(
) / 2
avgT
T
T
(49) ,EVAP 9 10 ,EVAP d q
Ex
Ex
Ex
Ex
(50) Where
Q
EVAP,m
i,Ex
q,EVAP,T
0,T
avg,Ex
d,EVAP andEx
ipresent evaporator heat flow rate, mass flow, thermal exergy rate, ambient temperature, average temperature, exergy destruction rate, and sate exergy rate , respectively.4.2.15 Turbine Analysis
Figure 4.15 illustrates schematic of the turbine. (Also, see Figure 3.1)
34 The following equations are used for the turbine.
33 35 36 isentropic
(
* (
)) /
TurbineW
m
h
h
(51) , ,3 35 36 d pump Turbine
Ex
Ex
W
Ex
(52) Where
W
Turbine,m
i,h
i,
isentropic,Ex
d,turbine andEx
ipresent turbine net work, mass flow, enthalpy, isentropic efficiency, exergy destruction rate, and sate exergy rate , respectively.4.2.16 Condenser Analysis
Figure 4.16 illustrates schematic of the condenser. (Also, see Figure 3.1)
Figure 16: Schematic of the condenser
The following equations are used for the condenser.
36
* (h
36h )
33 outcondQ
m
(23) ,condrankine(1
0/
) *
q avg outcondEx
T
T
Q
(54) 36 33 38 39
(
) / 4
avgT
T
T
T
T
(55) ,condrankine 36 38 ,condrankine 39 d q
Ex
Ex
Ex
Ex
Ex
(56)
Where
Q
outcond,m
i,Ex
q,condrankine,T
0,T
avg,Ex
d,condrankine,Ex
i andh
ipresent condenser heat flow rate, mass flow, thermal exergy rate, ambient temperature,35
average temperature, exergy destruction rate, sate exergy rate and enthalpy , respectively.
4.2.17 Pump 6 Analysis
Figure 4.17 illustrates schematic of the pump 6. (Also, see Figure 3.1)
Figure 4.17: Schematic of the pump 6
The following equations are used for the pump 6.
,6
(
33*
33* (
34 33)) /
pump isentropic
W
m
v
P
P
(57)
33 pump,6 34 d pump, ,6
Ex
W
Ex
Ex
(58) Where
W
pump,6,m
i,v
33,P
i,
isentropic,Ex
d pump, 6 andEx
ipresents pump work, mass flow, specific volume, pressure, isentropic efficiency, exergy destruction rate and sate exergy rate , respectively.4.2.18 Boiler Analysis
Figure 4.18 illustrates schematic of the boiler. (Also, see Figure 3.1)
36 The following equations are used for the boiler.
30
* h
30m * h
31 31 boilQ
m
(59) ,boil(1
0/
) *
q avg boilEx
T
T
Q
(60) 34 35 30 31
(
) / 4
avgT
T
T
T
T
(61) ,boil 35 34 ,boil d q
Ex
Ex
Ex
Ex
(62) Where
Q
boil,m
i,Ex
q,boil,T
0,T
avg,Ex
d,boil andEx
i present boiler heat flow rate, mass flow, thermal exergy rate, ambient temperature, average temperature, exergy destruction rate and sate exergy rate, respectively.4.2.19 Electrolyzer Analysis
Figure 4.19 illustrates schematic of the electrolyzer. (Also, see Figure 3.1)
Figure 4.19: Schematic of the electrolyzer
The following equations are used for the electrolyzer.
2
